Isotopes
What is an Isotope?
• Atoms with the same number of
protons and electrons but different
numbers of neutrons
• Many elements have two or more
isotopes
–Stable isotopes
–Unstable isotopes
Isotopes
• Can distinguish one form another by looking
at the mass number:
– Each number represents the mass number
• Oxygen has 3 isotopes: Oxygen-16, Oxygen-17, and
Oxygen-18
• Carbon has 3 isotopes: Carbon-12, Carbon-13, and
Carbon-14
Stable Isotopes
• An element whose nucleus does not
spontaneously give off particles or energy
• Of the known chemical elements, 80 elements
have at least one stable nuclei.
– These comprise the first 82 elements
from hydrogen to lead, with the two
exceptions, technetium (element 43)
and promethium (element 61), that do not have
any stable nuclei.
• Tin has ten stable isotopes
Unstable Isotope
• An element whose nucleus decomposes, or
decays, by losing particles and energy.
• Radioactive
• The energy or particles that are
emitted from the nucleus is called
radiation
• 3 Types of radiation: Alpha, Beta,
Gamma
• Used to determine the age of fossils
Example of Isotopes
• Carbon has three isotopes and they are
carbon 12, carbon 13 and carbon 14.
– Carbon 12 & 13 are stable isotopes
– Carbon 14 is an unstable isotope
Isotope Notation
How to write isotopes
• 1st-Element name-mass number
– Examples
• Oxygen has 3 isotopes: Oxygen-16, Oxygen-17, and
Oxygen-18
• Carbon has 3 isotopes: Carbon-12, Carbon-13, and
Carbon-14
• 2nd-
Calculating Isotopes
• You will use the mass number and the atomic number of
the isotope to determine the number of neutrons in the
nucleus.
• Neutrons=Mass number-atomic number
• Example:
– Oxygen has 3 isotopes:
• Oxygen-16
• Oxygen-17
• Oxygen-18
Each of these numbers represents the mass number
– Oxygen’s atomic number=8
– How many neutrons does each isotope of oxygen
have?
Calculating Isotopes
How many neutrons does each isotope below have?